Q: I want to add an efficient apartment to my house for my elderly mother. Can SIPS be used for large room additions or are they only for new construction? -- Betsy K.

A: "SIPS" stands for structural insulated panel system and it is very energy efficient. Although the panels are most often used for new house construction, they can be used for efficient room additions of any size.

What makes SIPS panels unique is the skins sandwiching the insulation foam between them are made of oriented strand board. This creates a very strong, highly insulated panel which is self-supporting. Once the panels are attached to the foundation and are connected together, the SIPS panels support themselves, the floors, ceiling, and roof.

SIPS panels are made with either Earth-friendly polystyrene or polyurethane foam between the skins. Polyurethane has a higher insulation R-value per inch thickness, so thinner panels provide the same insulation level (up to R-45) as thicker polystyrene ones.

What makes SIPS houses and additions extremely energy efficient are the high insulation levels and the airtightness. The panels can be made in lengths up to 24 feet, so there are very few joints to seal as compared to a typical stick-built lumber house. SIPS panels also block noise.

There are several methods for connecting the panels together. Vertical splines in grooves form a strong, airtight connection. Tongue-and-groove is another commonly used design. A cam-lock design uses cams and double grooves to draw the panels together.